Considerable efforts are expended by semiconductor manufacturers to improve product yield and reduce the frequency of defects in product manufacture. Difficulties in increasing product yield are exacerbated by the marketplace demand for technologically advanced product at reduced prices. For all but a narrow group of specialty product manufacturers, profits are obtained through high volume sales rather than through high profit margins. Accordingly, loss of product yield due to errors of manufacture, wafer mishandling and the like impact significantly upon the overall commercial success of the product.
Product yield loss can be experienced at virtually any stage of semiconductor processing. For example, loss can occur as a result of the failure to fully incorporate a process step into the manufacture of the semiconductor device, a deviation from established processing regimen, the use of defective reagents, problems in reagent application or deposition of films, and the like. Such deficiencies are typically not identified until the completion of device manufacture upon random product testing. The identification of a defective product from a given wafer can result in the discard of not only the semiconductor under test, but also the entirety of the wafer and its associated devices, as well as the batch of wafers that were processed in a like manner. Upwards of several thousand (but typically about 200) devices can be manufactured on a single wafer. Moreover, as wafers are typically processed in batches of 15 or more, the identification of a processing defect that relates to the entirety of a batch can result in a considerable economic loss. Further, such end of cycle testing can render it difficult to determine the precise nature of a product defect and the manner and process stage at which the defect was introduced into the wafer. In such instances, not only does the financial loss relate to the inability to sell manufactured product, there are also considerable losses experienced as a result of the expenditure of personnel time, chemical reagents, and processing apparatus on behalf of goods that cannot be commercialized.
In view of the foregoing deficiencies in the prior art of semiconductor processing, it would be desirable to provide semiconductor processing methods and apparatus which allow for the confirmation of properly applied and processed materials, such as patterned photoresist and other applied materials, at various stages of semiconductor processing in a manner which requires minimal interruption, in the processing regimen. Conventional wafer inspection procedures typically involve manually removing an exemplary wafer from its carrier boat and optically sampling a predetermined number of wafer sites to visually evaluate the wafer for the presence of defects. It would also be desirable to provide methods and apparatus for confirming the presence and satisfactory quality of a photoresist pattern and other applied materials which do not require physical contact with the semiconductor device under study. These and other advantages of the methods and apparatus of the present invention will become apparent by reading the following detailed description and drawings.